JP2020506290A - Transfer ring - Google Patents

Abstract

The invention relates to an apparatus for transporting a substrate in the form of a ring-shaped body (1) at least partially surrounding a ring opening. It comprises a first section (2) projecting radially outward with respect to the ring opening and a second section (3) projecting radially inward, each of the sections (2, 3) being the face of the ring opening. Have heat transfer properties that determine the axial heat transfer through those sections when there is an axial temperature difference with respect to the surface normal. At least one heat transfer characteristic of the first section (2) is such that the heat flowing in the axial direction through the unit area element is smaller in the first section (2) than in the second section (3). Is different from the thermal conductivity of the section (3), the thermal conductivity being the thermal conductivity or emissivity of at least one axially oriented surface of the section (2, 3). [Selection] Figure 2

Description

  The present invention relates to an apparatus for transporting a substrate in the form of a ring-shaped body at least partially surrounding a ring opening, comprising: a first section projecting radially outwardly with respect to the ring opening; A second section that projects into the ring opening, the sections having first and second heat transfer characteristics, the heat transfer characteristics being the axial temperature difference with respect to the surface normal of the surface of the ring opening. When there is, determine the axial heat transfer through those sections.

  From Patent Document 1, there is known a CVD reactor in which a plurality of substrate holders are arranged on a susceptor rotatably arranged in a process chamber. The substrate holder is placed in a temperature transmitting planar arrangement on the upwardly facing main surface of a susceptor that is heated from below. A substrate, in particular a semiconductor substrate, is placed on the upwardly facing main surface of the substrate holder, which is coated with a process gas supplied into a process chamber located above the susceptor. A gripper is provided for automatically placing the substrate on the substrate holder and removing it again therefrom, which has two gripping arms, which engage below the edge of the transport ring, the transport ring being attached to the substrate holder. And mounted from below on the outer edge of the substrate by a radially inward section. With the radially outward section of the transport ring projecting beyond the side surface defining the side edge of the substrate holder, the outward section of the transport ring can be engaged from below by the two gripping arms of the gripper.

  The coating process is performed in a process chamber whose upper wall is cooled, creating a temperature gradient between the heated susceptor and the process chamber ceiling. The temperature gradient causes a heat flow from the susceptor to the process chamber ceiling, which heat flow is due to high susceptor temperatures above 500 ° C., even in certain processes above 1000 ° C., by thermal radiation, and to the substrate holder and its It is also caused by heat conduction through the substrate placed on top.

  Another device is described in US Pat. However, in that case, the substrate is not placed on the second section of the transport ring. Alternatively, the transport ring carries a ring-shaped support element projecting radially inward, on which the outer edge of the substrate is supported.

International Publication No. 2012/096466 Published German patent application No. 10 2004 058 521

  The present invention aims to further improve the transport ring so that the layers deposited on the substrate can achieve higher lateral uniformity.

  In a general arrangement of transfer rings in a CVD reactor, a first section directed radially outward for support by a gripper arm of the gripper projects radially inward to engage the edge of the substrate from below. Heating to a lower temperature than the second section is shown in the model calculations. As a result of the heat transfer properties of the body forming the transfer ring, heat flows from the second section to the first section, resulting in a lower surface temperature in the edge region of the substrate than in the central region of the substrate. The substrate is arranged above the upwardly facing main surface of the substrate holder and is mounted in particular in contact with the main surface. This temperature difference causes other growth conditions to dominate in the edge region over the central region, resulting in a non-uniform stoichiometric composition of the layer deposited on the substrate, its thickness or its doping, at least in the edge region. Will have the property. Thus, on the transfer ring, on the one hand, by having a high thermal conductivity in the region carrying the edge of the substrate, the heat supplied from the susceptor flows to the edge of the substrate via the substrate holder and the transfer ring, whereby It is required to heat the edge of the substrate to the same temperature as the central area of the substrate is heated. On the other hand, it is required to minimize the heat loss from the section carrying the edge of the substrate in the transport ring to the section required for support on the gripper in the transport ring.

According to the invention, the sections of the body have different heat transfer properties. To define the distance, an imaginary axis extending in the direction of the plane normal to the plane of the ring opening at least partially enclosed by the body is assumed. The first section used for engagement from below by the gripper gripping arm is, according to the invention, a section which projects radially outwards. In particular, the second section, which forms the step of reduced thickness, is the section on which the edge of the substrate rests and which in the present invention projects radially inward. Heat transfer through the body takes place in the axial direction, i.e. from the downward main surface of the body to the main surface of the body facing the upper process chamber ceiling. The heat transfer property is in particular the heat conductivity of the section or the emissivity of the section surface. According to the invention, at least one heat transfer characteristic is such that the first section and the second section are different in that the heat flowing axially through the unit area element is smaller in the first section than in the second section. The section is different. Thus, the first section located radially outward has a greater heat flow resistance than the second section, which places the edge of the substrate in contact. Alternatively or in combination, the emissivity of the surface of the first section can be lower than the emissivity of the second section. The body forming the transport ring can be a ring. The ring-shaped body can form a closed or open ring. The first section can directly border the second section. The boundary between the first section and the second section may be in the region of an annular step of the substrate holder, on which the ring-shaped body rests. However, the boundary can also be located just above the edge of the substrate holder, ie the side of the substrate holder. However, the boundary can also be located in the region of the ring-shaped body projecting radially outward beyond the edge of the substrate holder.
In a development of the invention, it is proposed that the first section does not directly border the second section and that an intervening section extends between the first and second sections. This third section can have the same heat conducting properties as the second section, ie the section on which the substrate rests, ie in particular the same heat flow resistance. The boundary between the first section and the third section may be located at an annular step of the substrate holder. Alternatively, it may be located at the edge of the annular step or radially outside the annular step. The first section preferably projects completely beyond the substrate holder in the radial direction. Thus, it is heated by radiation from the surface of the susceptor by freely projecting beyond the side surfaces of the substrate holder.
The configuration of the conveying ring according to the invention results in a reduction in the dissipation of energy in the form of heat from the ring-shaped body over the prior art. Therefore, as a result that the edge temperature of the substrate does not greatly deviate from the central temperature of the substrate, the above-described cooling effect is reduced. A first section where heat is dissipated from the second section heated by contact with the substrate holder due to reduced heat conduction, substantially by radiation or by heat conduction through a gas present in the process chamber. The heat flowing to the air is reduced. It is specifically proposed that the upward main surface of the first section has a low emissivity, so that the energy release by radiation towards the cooled process chamber ceiling is also reduced.
It is preferable that the ring-shaped main body, which is a means for handling the substrate by the gripper, includes a plurality of components. In that case, the components have different heat transfer properties or their surfaces have different emissivity. Preferably, the first section is formed from one ring element having a low thermal conductivity or from a plurality of ring elements. Thus, the radially outer section has one or more ring elements of quartz, zirconium oxide or other material, thereby having a lower thermal conductivity compared to the material of the radially inwardly projecting section. The sections projecting radially inward can form a base body with high thermal conductivity. This base body can be made of graphite, silicon carbide or other good heat conducting materials.
Different emissivities cannot be defined solely by material selection. It is also possible to apply a different coating to the section surface. In particular, it is provided that the first section has a reflective element. The reflective element can be a metal piece encapsulated from the outside, in which case it can be encapsulated by a transparent material.
The first section can be made of one or more ring elements made of a transparent material and / or having a low thermal conductivity. The ring element encapsulates a reflective layer, which can be a metal layer. The emissivity of the surface of the first section can be less than 0.3. The emissivity of the surface of the second section and / or the third section is greater than 0.3. It here relates to a surface facing the process chamber ceiling. Thermal conductivity can differ by a factor of ten. Preferably, the thermal conductivity of the second section is at least ten times greater than the thermal conductivity of the first section. In a preferred variant of the invention, the base body is made of a good heat-conducting material, for example graphite or zirconium oxide, and extends over the entire radial width of the ring-shaped body. Thus, the base body forms the second section. The base body forms the carrying part of the first section, on which the ring-shaped element with low thermal conductivity and / or high reflectivity is arranged.
The first section and the third section together form a surface facing the process chamber ceiling. The first section also forms a surface facing the process chamber ceiling, wherein the surface of the first section is preferably at least twice as large as the surface of the third section. The boundary between the third section and the second section may be located in the area of the interface of the support area on which the edge of the substrate rests. Thus, the third section preferably has a greater axial thickness than the second section, in which case the first section preferably has the same axial thickness as the third section. . However, the first and third sections differ in their heat flow resistance.
In a preferred configuration of the invention, it is preferred that the ring-shaped body comprises a plurality of ring-shaped parts, which are arranged one above the other only in the radially outer region. These components can have different thermal conductivities. However, it is also provided that the ring-shaped body consists of a plurality of ring-shaped elements, in which case a gap is provided between the ring-shaped elements. According to the invention, the gap height is defined by the spacer element. Again, the ring element is preferably provided only in the radially outer region. The spacer element can be a projection that projects from the wide major surface of the ring element. However, the projection can also protrude from the wide main surface of the base body, whereby the ring element rests on the projection. Preferably, the protrusion has a hemispherical rising portion. The projection can be made from the same material as the base body or ring element.

FIG. 1 is a plan view of a susceptor mechanism of the CVD reactor. FIG. 2 is a sectional view taken along line II-II in FIG. FIG. 3 is a diagram in FIG. 2 of the second exemplary embodiment. FIG. 4 is a diagram in FIG. 2 of the third exemplary embodiment. FIG. 5 is a fourth exemplary embodiment of the present invention in FIG. FIG. 6 is a fifth exemplary embodiment in FIG.

Hereinafter, the present invention will be described in more detail with reference to exemplary embodiments.
The present invention relates to an apparatus for depositing a crystalline or amorphous layer, in particular a semiconductor layer, on a substrate 11, the lower surface of which rests on a support surface of a substrate holder 12. The broad lower major surface 14 of the circular disk-shaped substrate holder 12 rests on the upwardly facing surface 17 of the susceptor 16. The susceptor 16 is heated from below by a heating device (not shown).

  Above the substrate 11, there is a process chamber, into which a process gas is supplied by a gas inlet member (not shown). The process gas thermally decomposes either in the process chamber or on the surface of the heated substrate 11. The decomposition products react with each other, forming in particular a crystalline layer. It can consist of two, three or more components.

  The process chamber is bounded above by a process chamber ceiling 19 cooled by a cooling element (not shown).

  The susceptor temperature Ts is between 500C and 1000C. The temperature Tc of the process chamber ceiling 19 is in the range between 100C and 300C. As a result of this temperature difference, a vertical temperature gradient is formed between the surface 17 of the susceptor 16 and the process chamber ceiling 19, thereby causing heat to flow from the susceptor 16 to the process chamber ceiling 19. This is, on the one hand, due to thermal radiation, but also due to heat conduction through the substrate holder 12, the substrate holder 12 being made of a good heat conducting material, for example graphite.

  FIG. 1 is a plan view on the floor of a process chamber. A plurality of circular disk-shaped substrate holders 12, which are also not shown, are placed on a susceptor 16 which is not shown in FIG. 1 and is heated from below. Similarly, a ring-shaped main body 1 forming a transport ring is placed on an annular step portion 15 forming a support surface, which is not shown in FIG. Each substrate holder 12 is surrounded by intermediate members 21, 22, which fill the surface between the substrate holders and are made of a good heat conducting material, for example graphite. .

  For each of the substrate holder 12 and the transport ring 1, two substantially radially extending mutually parallel channels 23 are provided in the intermediate member 22, whereby the arms of the gripper, not shown, are connected to the ring-shaped body. In order to lift 1, it can be engaged from below the wide lower main surface of the first section 2 of the ring-shaped body 1. By mounting the edge of the substrate 11 on the second section of the ring-shaped body 1 projecting radially inward, the substrate 11 can be removed from the substrate holder 12 by lifting the ring-shaped body 1.

FIG. 2 shows a first embodiment of the transport ring 1. The first embodiment has a first section 2 that is a section 2 that is radially outward with respect to an axis passing through the opening surface of the conveying ring 1. The radially outer section 2 has a broad upper major surface 4 facing the process chamber 19 and a wider lower major surface 6 facing the susceptor 16, the lower major surface 6 being on a surface 17 of the susceptor 16. They are directly opposed and therefore receive the thermal radiation emitted by the susceptor 16. Heat Q ₁ is passed through the first section 2 in the axial direction, it is substantially released in the direction of the process chamber ceiling 19 from the upper major surface 4 through the heat radiation.

  The second section 3 projecting radially inward has a smaller axial thickness than the first section 2. The second section 3 has a wide downwardly directed main surface 7 on which the second section 3 rests on an upwardly directed annular step 15 of the substrate holder 12. An edge of the substrate 11 is placed on a wide upward main surface forming the support surface 5.

The substrate 11 is heated to the process temperature via thermal conduction by the substrate holder 12 and via thermal conduction by the support surface 13. The edge of the substrate 11 is heated by the heat flow Q ₂ through the second section 3, ie by the heat flow from the main surface 7 to the support surface 5. Since the heat conduction from the susceptor 16 to the first section 2 is smaller than the heat conduction from the susceptor 16 to the second section 3, heat flows from the second section 3 to the first section 2 and To the process chamber ceiling 19 due to thermal radiation. In order to prevent this vertical and radial heat flow in the conveying ring 1, the thermal conductivity of the second section 3 is greater than that of the first section 2.

  The second section 3 can directly border the first section 2.

  In that case, however, in the exemplary embodiment shown in FIG. 2, a third section 8 is provided between the first section 2 and the second section 3. The third section 8 has an upwardly-facing wide main surface 9, which is flush with the main surface 4. The downward broad major surface 10 of the third section 8 is flush with the major surface 6 of the first section 2.

  The second section 3 borders the third section 8 in the region of the vertical interface 20. The boundary surface 20 surrounds the area where the thickness of the second section 3 is reduced. The boundary surface 20 forms a step.

  The material properties of the second section 3 are substantially the same as the material properties of the third section 8. The material properties of the first section 2 differ from the material properties of the second section 3 in that the heat flow resistance of the first section 2 is greater than the heat flow resistance of the second section 3. In particular, the heat conduction characteristics of the second section 3 and, if necessary, the third section 8 are made larger than the heat conduction characteristics of the first section 2. The first section 2 and the second and third sections 3 and 8 can be made from different materials. The ring-shaped main body 1 can be composed of a plurality of members. The members can be connected to each other by a geometric connection or a mechanical connection. However, they can also be sintered together. Further, a plurality of parts may be used.

  In the exemplary embodiment shown in FIG. 2, the boundary between the first section 2 and the third section 8 and the boundary between the third section 8 and the second section 3 are the substrate holders. It is located above the twelve annular steps 15.

  The upward major surfaces 4, 9 and 5 and the downward major surfaces 6, 10 and 7 have an emissivity of infrared radiation and a reflectivity of infrared radiation. The emissivity of the surfaces 4, 6 assigned to the first section 2, at least the emissivity of the upwardly facing principal surface 4, is assigned to the principal surfaces 5, 7 and the third section 8 assigned to the second section 3. Smaller than the emissivity of the main surfaces 9 and 10 provided. In that case, at least the emissivity of the upward main surface 5 is larger than the emissivity of the upward main surface 4. Therefore, the principal surfaces 4, 6 have a greater reflectivity than the principal surfaces 5 and 7, and 9 and 10.

  However, it is sufficient that only one of the thermal conductivity properties of thermal conductivity, emissivity or reflectance differs.

  FIG. 3 shows a second embodiment of the present invention. In that case, the ring-shaped body 1 has a base body 24, which forms a second section, a third section and a lower area of the first section with a homogeneous material. The second section 3 differs from the third section 8 in that the axial thickness of the third section 8 is substantially greater than the axial thickness of the second section 3, whereby the support surface 5 Is adjacent to a vertical step 20 leading to the upper main surface 9 of the third section 8. The lower main surfaces 7, 6 are flush with each other.

  On the area of the base body 24, two ring elements 25, 26 made of a transparent material are arranged. The ring elements 25, 26 can be made of quartz. They have a lower thermal conductivity than the material of the base body 24, which can be made of graphite.

  A reflector is arranged between the two ring elements 25,26. It can be a metal film encapsulated between two ring elements 25,26.

  The metal film 27 is provided with an upward reflection of the second section 3 or the third section 8 by imparting a large reflectance to the first section 2 or the main surface 4 of the first section 2 facing the process chamber ceiling. Is given an emissivity smaller than that of the main surface 9 or 5.

  In the third embodiment shown in FIG. 4, the base body 24 forms a projection that extends to the radially outer edge of the transport ring 1 and, like the projection of the exemplary embodiment shown in FIG. An upward support surface is formed which extends at the level of the support surface 5 and is separated from the support surface 5 by a ring-shaped step of the third section 8.

  On this support surface of the first section 2 is mounted here a single ring element. The ring element 25 is made of a material having low thermal conductivity.

  It is proposed that the surface in the transport ring 1, especially the surface facing the cooled process chamber, has a different emissivity. The principal surface located radially outward has a low emissivity, and as a result, a high reflectivity. In contrast, the radially inner principal surface has a low reflectance and a high emissivity. In order to obtain stable thermal properties, the emissivity of the surface or surface coating should not be altered by chemical reactions or parasitic deposits. This is achieved by using a ring element made of a transparent material having a low thermal conductivity, for example quartz glass. The ring element is encapsulated with a reflective, in particular metallic layer, which is surrounded on all sides with a protective transparent material. The reflectivity should be greater than 60%.

  It is proposed that a ring-shaped web having a high thermal conductivity and thus a low heat flow resistance is arranged between the ring element made of a material with low thermal conductivity and the support surface 5. This increases the temperature in the edge region of the substrate and ensures that the substrate is also heated laterally by the web. The web forming the third section 8 is heated by heat conduction through the annular step 15. The surface of the first section 2 should be at least as large as the surface of the third section 8 and the radial width of the ring-shaped web forming the third section 8 should be at least 0.5 mm. is there.

  2 to 4, the substrate holder 12 is shown substantially mounted on the susceptor 16. However, the substrate holder 12 can be accommodated in a pocket of the susceptor 16. The substrate holder 12 can be provided rotatably with respect to the susceptor 16. For example, a gas outlet channel opens below the broad major surface 14 of the substrate holder 12, through which a purge gas is introduced into the interstitial space between the substrate holder 12 and the susceptor 16, which raises the substrate holder 12 up. A gas cushion to be placed is formed. With the proper flow direction of the purge gas, the substrate holder 12 can rotate.

  FIG. 5 shows an embodiment similar to that shown in FIG. The base body 24 forms a support surface located radially outward which is a substantially horizontal plane. The first ring element 25 rests on this support surface. The ring element 25 can be made of the same material from which the base body 24 was made. On the first ring element 25, a second ring element 26 is supported. The ring element 26 can be made of the same material from which the base body 24 was made. A gap 29 extends between the base body 24 and the first ring element 25 located directly above. The gap height of the gap 29 is defined by the spacer element 28. Each spacer element 28 is a rising portion starting from one of the two main surfaces between which the gap 29 extends.

  In the exemplary embodiment, each spacer element 28 is a hemispherical rising portion of the first ring element 25 on which the second ring element 26 rests. During operation of the device, gap 29 acts as a heat flow isolation gap.

  In a non-illustrated variant of the fourth exemplary embodiment, an additional spacer element can be provided to form a second gap between the first ring element 25 and the second ring element 26.

  The fifth embodiment shown in FIG. 6 substantially corresponds to the third embodiment shown in FIG. On the horizontal plane of the base body 24, a ring element 25, which can be made of the same material from which the base body 24 was made, is supported in a radially outer region. However, the materials of the base body 24 and the ring element 25 can be different from each other. The gap 29 between the lower main surface of the ring element 25 and the upper main surface of the base body 24 is important. The gap height of the gap 29 is defined by the spacer element 28. In the exemplary embodiment shown in FIG. 6, the spacer element 28 is formed by the ring element 25. It is a knob-shaped rise on the downward main surface. These knobs can have a hemispherical shape here.

  The embodiments described above are used to describe the invention as a whole, each of which independently advances the prior art with at least the following combinations, in which case two or more or all Combinations of these features of can also be combined:

  In that the heat flowing axially through the unit area element is smaller in the first section 2 than in the second section 3, at least one heat transfer characteristic of the first section 2 is such that the heat transfer of the second section 3 A device characterized by different characteristics.

  The device wherein the thermal conductivity is the thermal conductivity of the sections, wherein the thermal conductivity of the first section 2 is lower than that of the second section 3.

  The heat transfer characteristic is at least the emissivity of the surface of the sections 2 and 3 oriented in the axial direction, and the emissivity of the surface of the first section 2 is smaller than the emissivity of the surface of the second section 3. An apparatus characterized in that:

  An apparatus arranged between the first section 2 and the second section 3, characterized by a third section 8 whose thermal conduction properties substantially correspond to those of the second section 3.

  Apparatus characterized in that the second section 3 and optionally the third section 8 are mounted on an annular step 15 of the substrate holder 12.

  An apparatus characterized in that the substrate holder (12) is carried by a susceptor heated from below and the first section (2) projects freely beyond the side surface (18) of the substrate holder (12).

  A device characterized in that the ring-shaped body 1 comprises a plurality of interconnected elements 24, 25, 26, which have different heat transfer properties and / or are separated from one another by spacer elements 28.

  One or more ring elements 25, 26 assigned to the first section 2 have a low thermal conductivity, in particular made of quartz or zirconium oxide, and at least a base body 24 assigned to the second section is provided. A device having a high thermal conductivity and consisting in particular of graphite or silicon carbide.

  A device characterized in that the different emissivities of the surfaces are determined by different surface coatings or by at least one reflecting element 27.

  One or more ring elements 24, 25 assigned to the first section 2 are made of a transparent material having a lower thermal conductivity, in which the reflective layer 27, in particular a metal layer, is encapsulated. And equipment.

  The thermal conductivity of the second section 3 is at least 10 times the thermal conductivity of the first section 2 and / or the emissivity of the surface 4 of the first section 2 is less than 0.3; And an emissivity of the surfaces 5, 9 of the second section 3 and / or the third section 8 is greater than 0.3.

  The ring-shaped body 1 is formed from a base body 24 extending over the first section 2 and the second section 3, the first section 2 having different heat conducting properties than the base body 24. Has at least one ring element 25, 26

  The first section 2 and the third section 8 each have a surface 4, 9 facing the process chamber ceiling 19, the surface 4 of the first section 2 being at least twice as large as the surface 9 of the third surface 8. A device having a size of

  The surface 5 of the second section 3 facing the process chamber ceiling 19 forms a support area for supporting the edge of the substrate 11, which support area is surrounded by an interface 20 of the third section 8. The third section 8, like the second section 3, is mounted on the annular step 15 of the substrate holder 12 by surfaces 10, 7 facing the susceptor 16. And equipment.

  All features disclosed (individually, but in combination with each other) are essential to the invention. The disclosures of the related / attached priority documents (copies of the prior application) are also fully incorporated into the disclosure of the present application in order to include the features of these documents in the claims of the present application. The dependent claims are characterized by their composition independent of the development of the invention from the prior art, in particular for filing a divisional application of these claims.

DESCRIPTION OF SYMBOLS 1 Ring-shaped main body 2 1st section 3 2nd section 4 Main surface 5 Support surface 6 Main surface 7 Main surface 8 Third section 9 Main surface 10 Main surface 11 Substrate 12 Substrate holder 13 Contact surface 14 Main surface 15 Support Surface, annular step 16 Susceptor 17 Surface 18 Side surface 19 Process chamber ceiling 20 Boundary surface 21 Spacer 22 Spacer 23 Channel 24 Base body 25 Ring element 26 Ring element 27 Reflection element 28 Spacer element 29 Gap Ts Susceptor temperature Tc Process chamber ceiling temperature Q ₁ Heat flow Q ₂ Heat flow

Claims (16)

Substrate transport in the form of a ring-shaped body (1) mounted on an annular step of a substrate holder (12) carried by a heated susceptor (16) and at least partially surrounding a ring opening The device having a first section (2) projecting radially outward with respect to the ring opening, and a second section (3) projecting radially inward.
The first section (2) has a first upwardly directed upper major surface (4) and a first downwardly directed lower major surface (6) and the first section (2) is radially outward. Receiving a first heat flow (Q ₁ ) from the surface (17) of the susceptor (16) by thermal radiation, projecting beyond the substrate holder (12), and
The second section (3) forms a support surface (5) on which the edge of the substrate (11) rests by means of a second upwardly directed upper major surface, and an upwardly directed annular step. By having a second downwardly directed lower major surface (6) resting on (15), the edge of said substrate (11) is subjected to a second heat flow (Q ₂ ) via a second section (3). Heated by
When there is an axial temperature difference with respect to the surface normal of the surface of the ring opening, each of said sections (2, 3) is separated from each lower main surface (6, 7) through the respective section by a respective upper main surface ( 4) having a heat transfer characteristic for determining axial heat transfer to 4),
At least one heat transfer characteristic of the first section (2), in that the heat flowing axially through the unit area element is smaller in the first section (2) than in the second section (3). Is different from the heat transfer characteristic of said second section (3).   The thermal conductivity of the section is the thermal conductivity of the section, and the thermal conductivity of the first section (2) is lower than that of the second section (3). An apparatus according to claim 1.   The heat transfer characteristic is the emissivity of at least the axially oriented surface of the section (2, 3), and the emissivity of the surface of the first section (2) is the second section (3). 3. The device according to claim 1, wherein the emissivity is lower than the surface emissivity.   A third section (8) disposed between the first section (2) and the second section (3), wherein the heat transfer characteristic substantially corresponds to that of the second section (3). 4. The device according to claim 1, wherein:   5. The device according to claim 1, wherein the second section and, if necessary, the third section are mounted on an annular step of a substrate holder. An apparatus according to any one of the above.   The substrate holder (12) is carried by a susceptor (16) that is heated from below, and the first section (2) projects freely beyond the side surface (18) of the substrate holder (12). The device of claim 5, wherein   Said ring-shaped body (1) consists of a plurality of interconnected elements (24, 25, 26), which have different heat conducting properties and / or are separated from one another by spacer elements (28). The apparatus according to any one of claims 1 to 6, wherein:   One or more ring elements (25, 26) assigned to said first section (2) have a low thermal conductivity and especially consist of quartz or zirconium oxide, and are assigned at least to said second section Device according to any of the preceding claims, characterized in that the provided base body (24) has a high thermal conductivity and consists in particular of graphite or silicon carbide.   9. The device according to claim 3, wherein the different emissivities of the surfaces are determined by different surface coatings or by at least one reflecting element (27).   One or more ring elements (24, 25) assigned to said first section (2) are made of a transparent material having a lower thermal conductivity, in which a reflective layer (27), in particular a metal layer, is provided. Device according to any of the preceding claims, wherein the device is enclosed.   Device according to any of the preceding claims, wherein the thermal conductivity of the second section (3) is at least 10 times greater than the thermal conductivity of the first section (2).   The emissivity of the surface (4) of the first section (2) is less than 0.3 and the radiation of the surface (5, 9) of the second section (3) and / or the third section (8). Apparatus according to any of the preceding claims, wherein the rate is greater than 0.3.   The ring-shaped body (1) is formed by a base body (24) extending over the first section (2) and the second section (3), wherein the first section (2) Device according to any of the preceding claims, characterized in that the device comprises at least one ring element (25, 26) having a different heat transfer characteristic from the base body (24).   Each of the first section (2) and the third section (8) has a surface (4, 9) facing the process chamber ceiling (19) and the first section (2). Device according to any of claims 4 to 13, characterized in that the surface (4) is at least twice as large as the surface of the third section (8).   The surface (5) facing the process chamber ceiling (19) in the second section (3) forms a mounting area for mounting an edge of the substrate (11), Are surrounded by a boundary surface (20) of the third section (8), and the third section (8), like the second section (3), is surrounded by the susceptor (16). Device according to any of the preceding claims, characterized in that it is mounted on an annular step (15) of the substrate holder (12) by a surface (10, 7) facing away from the substrate.   An apparatus characterized by one or more features of the preceding claims.

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